Age hardenable, low expansion, nickel-iron-titanium alloy



A. M. TALBOT Dec. 16, 1941.

I AGE HARDENABLE, LOW EXPANSION, NICKEL-IRON-TITANIUM ALLOY Filed 001;. 2'7, 1939 2 Sheets-Sheet 1 7Q NowCARammfi-rAmuM IOOO BOO

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TEMPERATURE "F IVNVENTOR HLBERT M 777280? ATTORNEY Patented Dec. 16,1941 I UNITED STATES PATENT v oer-lea Albert M. Talbot, Fail-haven, N. 1.. amino: to

' The International Nickel Company, Inc New York, N. Y., a corporation of Delaware Application October 27, 1939, Serial No. 301,580 3 Claims. (01. 148-31) with about 36% nickel havevery low coeflicients of expansion, which approach zero for a temperature range up to about 300 or 400 F. As the nickel content is decreasedfrom 36%, the coeflicient of expansion rises rapidly above that obtained with 36% nickel and the temperature range of low expansivity is lowered. On the other hand, as the nickel content is increased above 36%,. the coefl'icient of expansion rises more slowly and at the same time, the temperature range over which the alloy will display low expansion characteristics is raised. It is possible by regulating the nickel content between about 36 and 50% to obtain any desired coefllcient of expansion between 0.5x 10- per F. and 5.5x 10-- per F. The various properties of these ironnickel alloys are well known and amply described in the literature, e. g., Scotts article in Transactions of the American Society for Steel Treating, vol. 13, 1928, p. 829. The low expansion ironnickel alloys are known under various trademarks. The 36% nickel alloy is known as Invar, while the. 46% nickel alloy has the same coeflicient as platinum .and is known as Platinite. These austenitic alloys can be hardened by cold work. When the alloys were' hardened only by cold work, many potential applications were limited by the fact that the ordinary alloys did not possess the required high strength, hardness, elastic properties, wear resistances, etc. It was known that appropriate amounts of titanium will confer age hardenability upon a broad range of austenitic nickel-iron and iron-nickel alloys. When titanium was incorporated in the 36% nickel alloy to impart age hardenability thereto, certain shortcomings were encountered with regard to the expansion properties.

Although many attempts were made. to remedy the aforementioned shortcomings, none, as far as I am aware, was entirely successful, produced satisfactory results and could be carried into practical and economic industrial scale operation.

I have discovered that in spite of the presence of titanium it is possible, by critically adjusting the nickel and titanium contents in iron-nickel alloys to provide predetermined expansivity characteristics and to provide low expansivity coupled with high mechanical properties, including hard ness, which make the new alloys applicable in many situations where the straight iron-nickel alloys were entirely unsuitable due to their low hardness and particularly their low yield point.

It is an object of the present invention to provide improved age hardenable iron-nickel alloys with predetermined low expansion characteristics which contain controlled and adjusted proportions of nickel, carbon and titanium and in which the nickelis balanced against the titanium and the carbon.

It is another object ofv the present invention to provide age hardenable low expansion ironnickel alloys containing titanium and characterized by improved mechanical properties, including high tensile strength and high hardnesses, while still being able to control the expansion characteristics by proper control of the chemical composition.

It is a further object of the present invention to provide age hardened articles of manufacture made of low expansion iron-nickel-titanium alloys in which the nickel is adjusted in special proportions to compensate for the modification in expansion properties caused by the introduction of titanium into the alloy.

The invention contemplates a method of producing age hardenable iron-nickel alloys containing controlled amounts of titanium, and articles of manufacture made therefrom, possessing predetermined expansion properties combined with high mechanical properties in the age hardened condition, said process involving an adjustment, in special proportions, of the nickel content to compensate for the modification in expansion properties caused by titanium.

Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a graph illustrating the efiect of noncarbidic titanium upon the hardness of ironnickel alloys;

Fig. 2 is a graph depicting a typical expansion curve;

Fig. 3 is a graph depicting the influence of effective nickel upon the minimum coefflcient of Broadly stated, the invention provides improved iron-nickel alloys of predetermined expansion characteristics which contain controlled amounts of titanium and which after an age hardening heat treatment possess markedly increased mechanical properties, including tensile strength and hardness, and exhibit predetermined expansion properties in the hardened condition. I have discovered that when titanium is added to iron-nickel alloys of the Invar type to render the alloys age-hardenable the expansion properties are adversely affected and are very sensitive to the composition of the alloy with the consequent result that the expansion properties are not as expected or desired. It has been found that the minimum expansion properties of the titanium-containing alloys are not simply dependent upon the total nickel content of the alloy, as is the case in ordinary ironnickel alloys, but are dependent upon the portion of the nickel content which has been termed herein the effective nickel content. I have found that the total nickel content must be properly balanced against the alloying elements, particularly titanium, in a special manner so that the effective nickel content has a predetermined value for given expansion characteristics.

It has been found that certain factors must be applied against the total nickel content in order to have the proper effective nickel content present in the alloy. These factors are dependent upon the various elements in the alloys. In addition to titanium, the alloys may contain carbon, especially in industrial practice. While not a necessary element, present commercial production methods prevent the complete exclusion of carbon. The primary governing factor in determining the relation between total and effective nickel content in the alloy is the amount of available titanium, which is herein termed "non-carbidic titanium. For practical purposes, the non-carbidic titanium is the total titanium content in weight percent less four times the carbon content in weight percent. This gives the percent of titanium that is not combined with carbon as the compound, TiC. For economy as well as for the undesirable effects of carbon on the expansion characteristics, the carbon should be kept as low as possible in alloys which are to exhibit the lowest expansivity. The effective nickel content which determines the expansion properties and characteristics of the alloy may be expressed by the following formula:

Effective Ni=Total NiK(Non-carbidic Ti) In this equation, K is a constant with a value of about 2.4; and for practical purposes, Nonearbidic Ti is equal to Ti-4X0; and Ni, Ti and C are nickel, titanium and carbon, respectively, in weight percentage.

The desired Brinell hardness and related mechanical properties determines the titanium content. The desired minimum expansion characteristics determine the effective nickel content which is related to the total nickel content as expressed by the following formula:

In carrying the invention into practice, the compositions of the alloys fall within the approximate ranges given in Table I in balanced proportions as expressed by the formula set forth hereinbefore.

As pointed out hereinbefore, carbon need not be, but usually is, present due to commercial production methods. It is to be understood that carbon may be completely absent or may be present only in traces or small amounts of the order of 0.001%. In addition to the elements nickel, iron and titanium, and usually carbon, the alloys may also contain small amounts of minor elements and impurities, and when I say in the specification and claims that the balance is iron, balance is substantially all iron, etc., I include within the expression minor constituents and impurities, such as cobalt, manganese, silicon, aluminum, sulfur, phosphorus, and other elements commonly present in such materials in commercial practice. Cobalt in appropriate amounts may be beneficial. It is well known that amounts of the order of 5% cobalt are beneficial in ordinary iron-nickel alloys of the Invar type. The alloys may also contain from traces, say 0.001%, up to possibly 1.5% manganese, up to about 1.5% silicon, up to about 1.0% aluminum,'etc. From about 0.2% to 0.5% manganese is usually present for forgeability, although about 0.05% calcium may be a desirable alternative addition. Aluminum and silicon are commonly present in commercial ferro-titanium and are often introduced into the alloy along with the titanium. Although silicon contents up to about 0.9% have been used, the silicon content is preferably held to less than about 0.3%, e, g., 0.1 to 0.2%, and the aluminum content does not usually exceed about 0.5%, e. g., 0.3%.

More specifically when the lowest expansion properties are desired it is preferred to regulate the nickel, carbon, titanium and iron content in amounts to give the compositions set forth in Table II in accordance with the balanced proportions set forth by the formula given hereinbefore.

Table II Element Percentage Effective nickel .percent Total nic d Total titanium. Carbon Irrm After an age hardening treatment the alloys of the present invention possess markedly increased mechanical properties and then exhibit the desired low expansion properties. Thus, Brinell hardnesses as high as 400 are developed after age hardening heat treatment as compared to Brinell hardnesses of about for ordinary, titaniumfree, iron-nickel alloys containing about 36% nickel. The maximum physical properties, particularly the proportional limit, obtainable in a fully aged alloy depends upon the amount of noncarbidic titanium present in the alloy. In general, the mechanical properties of aged material increase with the non-carbidic titanium. Fig. 1 shows the effect of non-carbidic titanium upon the maximumgis reached at about 3.25% noncarbidicvtitani'um since further increases in noncarbidic 'titanlrun produce only slightly' higher hardnesses and increase the, cost. and diiilculty of manufacture. iumcontent lowers the inflection temperature.

A'high inflection temperature'is desirablebecause 'this means that the minimum expansion region extendsto a higher .temperature. Fig. 2 is a graphofatypical expansion curve showing the inflection temperature and the range'of minimum expansivity. .An increase in the 'non -c'arbidic titanium also raises the general level of expansivity as shown in Fig. 3, and the over-all expansion through a range of temperatures, and raises the total nickel content required to secure the lowest expansivity. InFig. 3 the influence of effective nickel content on'the minimum coeflicient of expansion at two non-carbidic titanium levels is shown. It will be apparent that a balance must be made between the desired hardness or other mechanical property and the desiredlow expansion properties where, for instance, expansivities below 2x per F. are required, and that only the amount of non-carbidic titanium necessary to give the desired hardness or other mechanical property should be used. The most favorable balance between properties is had by limiting the non-carbidic titanium content to the lowest amount sufllcient to give adequately high mechanical properties. Thus, where. it is desired that the alloy have a very high'hardness, e. g., 365 Brinell hardness, in combination with the lowest possible minimum coefficient of expansion at that level of hardness, a non-carbidic titanium observed from Fig. 3 that the curve becomes comparatively flat in the vicinity of the lowest minimum coeflicient of expansion and that a range of effective nickel contents is available which yield substantially similar minimum expansion properties, however, it is preferred to use the higher effective nickel contents in this range since the alloys of higher effective nickel content have higher inflection temperatures. It has been found that the inflection temperature bears no obvious relation to the total nickel content within the ranges contemplated but is simply related to the effective nickel content. This relationship between effective nickel and inflection temperature is showngraphically in Fig. 4. Aluminum has no substantial effect upon the minimum coeflicient of expansion but lowers the inflection temperature. Silicon causes an increase in the minimum coefilcient of expansion in addition to lowering the inflection temperature. Accordingly, where silicon and/or aluminum must be present, aluminum should be used in preference to silicon and the silicon content held at a low value, e g.,

0.1% to 0.2%. Manganese increases the mini- Increasingthe non-'carbidic'titanv mum coefficient. of expansion and preferably only thatamount required to insure forgeability should be present in the alloy, e. g., 0.3% to 0.5% manganese.

The alloys of the presentinvention or minimum expansion properties and characteristics after agejhardening heat treatment. This heat treatment comprises a high temperature solution treatment followedby rapid cooling, e. g., quenching, and then an aging treatment at lower temperatures to eflect precipitation of the hardening constituent in a finely divided state followed'by; cooling, preferablyra'pid cooling, to at mospheric temperatures. The solution treatment is usually carried out at temperatures within the range of 1650" F. to1825f, F., the lower. temperatures being preferably employed for alloys-with low non-carbidic titanium" contents. Lower temperatures may be' used, especially with low titanium contents, but more time is required to soften the alloys. The solution temperatures preferably employed are shown in Fig. 5 and lie ina band extending from. about 1650" F. to 1725 F. for 1% non-carbidic titanium to about 1750 at these temperatures is usually satisfactory, although still longer times are desirable for eastings and temperatures of the order of 2000 to 2100" F. may be used. After solution heat treatment the alloys are rapidly cooled. Oil quench ing is satisfactory for most section sizes to insure full softening and, of course, a water quench may be used. In general any cooling from. solution temperatures which is sufliciently rapid to produce a softened alloy, 1. e., an alloy having a hardness not exceeding about to Brlnell will be satisfactory. Slow cooling from the solution temperatures results in full hardening, but where lowest expansivity is required this is not a desirable method of obtaining hardening due to the undesirable effects of this method on, the expansion characteristics. It has been found that a rapid cooling rate is necessary to obtain the lowest expansion characteristics. The aging treatment is carried out within the somewhat narrow and critical temperature range of 1100 F. to 1325 F. for from about 1 to about 24 hours. 50 The aging temperature preferably increases with the amount of the non-carbidic titanium. The preferred aging temperatures are shown in Fig. 5 and lie in a band extending from about 1100" F. to 1150 F. at 1% non-carbidic titanium to about 5 1250" F. to 1325" F. at 4.25% non-carbidic titanium. The alloys are preferably aged for about 8 to 12 hours although by far the'majority of the hardening occurs within the first hour. Low titanium-containing alloys, e. g., about 1% noneo carbidic titanium, requir longer aging periods up to 24 hours. In general, aging is more rapid as the non-carbidic titanium increases. 'Iypical examples of satisfactory aging temperatures for various non-carbidic titanium contents in al- 5 loys of the present invention are given in Ta ble III. I 7

Table III possess low F. to 1825 F. for 4.25% non-carbidic titanium. A solution heat treatment of about 2 to 3 hours Aging for 2 or 3 hours at each of a plurality of successively lower temperatures produces substantially similar hardening to aging 8 to 12 hours at a single proper temperature. After the manner the best possible expansion properties are obtained in combination, with the desired high mechanical properties. It appears that any treatment that produces internal stresses is aging treatment, the alloys may be cooled in any beneficial in reducing the coefllcient of expanmanner but it is preferred to rapidly cool, e. g., sion. The maximum aging response in cold water quench, since this produces lower coefiiworked material is obtained by aging at slightly cients of expansion than are observed after slow lower temperatures, e. g., 50 F. lower, than at cooling. Satisfactory solution temperatures and t eg a aging pe a es ut the latter aging temperatures for wrought alloys containtemperatures may be used to give very satising various percentages of "non-carbidic titanifactory results and substantially the same reum are shown graphically in Fig. 5. A satis- Sults y be o ed in ghtly less time. The factory heat treatment for a wrought iron-nickel minimum eeemeient of expansion 01 a d d alloy containing about 2.75% noncarbidic t t niquenched material produced in accordance with um (2.81% total titanium) in accordance with 15 the present invention is not materially increased the present invention comprises heating for about by heating a Short time D to p a u 2 hours at about 1100" F. followed by oil quenchof about or for a s e a te peraing and aging at about 1250 F. for about 9 hours. tures D to 0 s, heating ged maten t mechanical properties do t, reach rial oi the present invention for ten days at their maximum values after the same aging time. resulted y in a y sli c ease The proportional limit reaches its maximum valin the minimum eeemeient 01' expansion, 1. e., ues early during the aging period and then defrom D to X D l r creases slightly upon further aging whereas the Materials having the compositions contemtensile strength and hardness reach a maximum plated by the P se vention may be worked in value at about the normal aging time and the the usual manner into Products Possessing high yield point continues to rise slightly when aged mechanical P pe combined witl'ilow exbeyond normal times. For example, the proporpension a cteristics. Forging operations are tional limit of an alloy containing 24 preferably carried'out at temperatures of about carbidic titanium was raised from about 22,000 1800 to about 2300 followed by que ing pounds per square inch to a maximum of about rapld ooolmg Where o ed e al is de- 76,000 pounds per square inch after one hour of sued? Representative eppexi'mate ues for aging whereas the tensile Strength was raised the properties obtained in material of the Invarfrom about 30,000 pounds per square inch to type madein accordance with the present invenabout 142,000 pounds per square inch in about tlon are given in Table IV. Proportional limits one hour of, aging and to a maximum of about 6 to 701000 Pounds Per Square inch ere 160,000 pounds per squareinch after about nine readily developed in comparison t about hours of aging. The yield point of the alloy was Pounds P equate inch for Ordinary Inraised from about 42,000 pounds per'sq'uare inch Var-type alleysto about 98,000 pounds per square inch in about 0 Table IV one hour, to about 114,000 pounds per square inch in about nine hours and to about 118,000 pounds 4 per square inch in eighteen hours. Property Aged condition Ithas been found that the effect of cold work is decidedly beneficial upon the properties of the 45 Tensile men alloys. Cold work has the effect of reducing the Yield F e 1 :3 231%) 90? 1390? minimum coeflicient of expansion and has 20,000 to 32000 52000) 75000 greater effect if applied before aging'than after g g l 130w 6 223w aging. Cold working before aging also raises 9 p ereentu 12 to 00; 30m 18. the final hardness as much as 40 to Brinell g9e 43 17 to ardness numbers with'2o% to 40% or more of eigntiifnfgii fifi to cold reduction. This treatment gives the maxi- Inflecti? temvoratur: o a mum hardness attainable in a particular alloy. 500 Cold working after aging is less eflective and raises the hardness up to about 20 Brinell hard- In order that those skilled in the art may have mess with 20% ormore cold reduction It is a better understanding of the present invention, fen-ed t obtain a desired hardness by cold illustrative examples are given in Table V of the working and aging an alloy rather than by incomposition and Properties of e hardened creasing the non-carbidic titanium content alloys mode in accordance with the p se t inand then aging without cold working. In this vention.

Table V Nickel Titanium Alloy Carbon a i i'n i i i gg gg tfii n Actual Effective Actual gg j Xl0"/F. emp- Percent Percent Percent Percent Percent o F The present invention provides a method ofnickel alloy a selected titanium content within said range such that Ti minus 4 C lies between about 1% and 4.25%, the selected titanium content corresponding to the predetermined desired mechanical properties, for example, the desired hardness, and being larger the higher said desired properties; the nickel content of said alloy being proportioned within said range in accordancewith the following formula:

Total Ni=Eifective Ni +K(Ti-4 x C) where the efiective nickel is selected within the ranges of about 32% to about 50% to correspond to the predetermined desired low expansion characteristics, K being a constant having a value of about 2.4, and Ni, Ti and C being respectively the weight percentage of nickel, titanium and carbon, whereby an improved age hardenable iron-nickel alloy is obtained combining low expansion properties with high mechanical properties, including high hardnesses, in the age hardened condition.

The present invention contemplates improved age hardenable andage hardenedarticles of manufacture made of the alloys of predetermined low expansion characteristics provided by the present invention. Typical illustrative examples of uses for east and wrought alloys of this type where strength, high proportional limit hardnessor wear resistance are required combined with predetermined low expansion characdies; reamers; boring bars; gauges; machine parts including glass machines; lead screws; valves; Diesel injector pumps and valves; thermostats; rolls; rolling mill frames and screw downs; platinum, tantalum and glass lined autoclaves and clad materials; diamond and carbide tipped tool shanks including drills; proportioning pumps and meters; and for highly polished articles, such as reflectors, where the ease of polishing of a hard material is important, as is the absence of warping in subsequent use.

I am aware of the invention described in U. S. patents to Pilling and Merica, including U. S. Patent No. 2,043,163, and I do not claim any of the subject matter disclosed therein. The present invention is an improvement in the art of low expansion iron-nickel alloys.-

Although the present invention has been described in conjunction with preferred embodiments, it is understod that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as

those skilled in the art will readily understand.

I claim:

1. As an article of manufacture, an age hardened iron-nickel-titanium alloy having minimum coefiicient of expansion and containing in weight percentage 39.3% to 44.3% nickel; 2% to 3.5% titanium; 0.001% to 0.07% carbon; the percentage of titanium and carbon being such that Ti minus 4 x0 lies between 2% and 3.25%, and the percentage of nickel, titanium and carbon being such that lies between 34.5% and 36.5%, K being a constant having a value of about 2.4 and Ni, Ti and C being respectively nickel, titanium and carbon in weight percentage; and the balance being substantially all iron whereby a novel age hardened iron-nickel-titanium alloy is obtained having a unique combination of properties, including minimum coefficient of expansion and inflection tempertaures above approximately 250 F. to-

gether with high hardness exceeding about 225 Brinell.

2. The article of manufacture set forth in claim 1 constituted of the alloy which has been lies between 2% and 3.25%, and the percentage of nickel, titanium and carbon being such that Total NiK(Ti-4 X C) lies between 34.5% and 36.5%, K being .a constant having a value of about 2.4 and'Ni, Ti and 0 being respectively nickel, titanium and carbon in weight percentage; and the balance being substantially all iron whereby a novel age hardenable iron-nickel-titanium alloy is obtained having in the aged condition a unique combination of properties, including minimum coeflicient of expansion and inflection temperatures above approximately 250 F. together with high hardness exceeding about ,225 Brinell.

ALBERT M. TALBOT. 

